The association between acute rejection, acute tubular necrosis, good function and relative infiltration of CD56 subsets of both CD8+ and CD4+ T cells was examined on 67 samples of graft infiltrating cells (GIC) and corresponding peripheral blood lymphocytes (PBL) obtained from renal allograft recipients. Quantification of cell subset profiles was determined by two-color flow cytometry. While a high proportion of CD4+CD56+ GIC was detected when both renal dysfunction and graft cytopathology (acute tubular necrosis or acute rejection) were present, this cell subset was undetectable in peripheral blood. In contrast the CD8+CD56+ T-cell subset was not discriminatory. The presence of CD4+CD56+ cells among freshly-isolated lymphocytes from renal allografts supports the idea that the local environment is involved in the selection of this subset, thus participating in the amplification of the immune-response. In addition, a homing of this T-cell subset into the transplanted organ may constitute an early sign of graft immunopathology.